Hybrid vehicles, such as plug-in hybrid vehicles, may have two modes of operation: an engine-off mode and an engine-on mode. While in the engine-off mode, power to operate the vehicle may be supplied by stored electrical energy. While in the engine-on mode, the vehicle may operate using engine power. By switching between electrical and engine power sources, engine operation times may be reduced, thereby reducing overall carbon emissions from the vehicle. However, shorter engine operation times may lead to insufficient engine coolant temperature maintenance.
Various strategies have been developed to address coolant temperature management in hybrid vehicle systems. As one example, waste exhaust heat may be recovered to more rapidly increase engine coolant temperature. For example, during cold start engine idle conditions, various systems may utilize waste engine heat to hasten engine warm-up, thereby enabling improved emission performance, engine efficiency, etc. Likewise, waste heat in the engine cooling system and/or lubricating system may be directed to the cabin for cabin heating or to the lubricating system, thereby reducing lubricant viscosity thus reducing friction.
For example, US 2011/0239634 describes a heat exchanger recovery unit that allows for exhaust heat to be recovered from an exhaust system. The system includes a first and second flow passages that each recovery heat from different areas of the exhaust system. Further, the first and second flow passages each include a control valve to selectively communicate the first and/or second flow passage with their respective component of the exhaust system. Through actuation of the control valves, the heat exchanger recovery unit can maintain coolant temperature.
The inventors herein have recognized various issues with the above system. In particular, closing a valve results in stagnant coolant, which also isolates coolant from recovering heat from the exhaust system and thus transferring the recovered heat to engine components that need warming is inhibited.
As such, one example approach to address the above issues is to utilize an exhaust manifold that includes an integrated coolant passage that passively enables coolant flow while a vehicle is in operation. Such an approach allows coolant to continuously circulate through the coolant passage to increase a heat exchange rate while balancing a contact area between the coolant passage and the exhaust manifold. The coolant passage may be in direct surface contact with an exterior surface of an exhaust manifold to recover heat through conduction. The coolant passage is arranged such that an upstream portion of the coolant passage wraps around an outlet of the exhaust manifold. This arrangement allows for an increased heat exchange rate. Further, the coolant passage includes a downstream portion that closely matches a contour of a top surface and a bottom surface of a plurality of runners of the exhaust manifold. In this way, the coolant passage contacts the exhaust manifold to recover exhaust heat from the exhaust manifold via conduction more efficiently that previous approaches due to the resulting compact geometric configuration.
Note that various coolant passages may be included. Further, the coolant passages may be fluidically coupled such that coolant flow may cycle through the heat recovery system. Further still, the exhaust manifold assembly may include various apertures to reduce contact area between the heat recovery system and the exhaust manifold, if desired.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.